Coordinative chain transfer polymerization (CCTP) using main group metals, i.e. a reversible chain transfer of polymeryl chains between chain growth active metal centers and chain growth inactive metal centers, has become an important strategy in insertion polymerization to reduce the amount of polymerization catalysts, to control the molecular weight and molecular weight distribution of polymers as well as to introduce chain end-functionalization by appropriate quenching of main group metal polymeryls. See Valente et al., Chem. Rev. 2013, 113, 3836-3857; Jian et al., Chem. Commun. 2010, 46, 3022-3024; German et al., Angew. Chem. Int. Ed. 2013, 52, 3438-3441. (b) Norsic et al., Angew. Chem. Int. Ed. 2015, 54, 4631-4635; Makio et al., J. Am. Chem. Soc. 2013, 135, 8177-8180.
Most commonly, commercially available un-functionalized aluminum and zinc alkyls have been employed, with zinc alkyls much better performing in terms of transfer efficiency and, thus, molecular weight control. With respect to heteroatom-functionalized main group metal alkyls, recently homoleptic di(cw-aminoalkyl) magnesium reagents have been used as chain transfer reagents to yield end functionalized amino polyethylenyl magnesiums (Ottou et al., Macromolecules 2017, 50, 8372-8377.) Functionalized magnesium reagents were also employed to initiate polybutadiene chain growth to end-functionalized high trans polybutadiene (Leicht et al., Macromolecules 2018, 51, 763-770), or with increased chain transfer numbers, to functionalized polybutadienes of less uniform stereochemistry (WO201013945).
In contrast, both in organic synthesis and in polymer chemistry, heteroatom-functionalized aluminum reagents have scarcely been used as synthetically useful reactants for the transfer of functional group substituted carbon nucleophiles probably owing to drawbacks in the synthesis of homoleptic aluminum alkyls or the expectedly low chemoselectivity of mixed aluminum alkyls (Xu et al., Acc. Chem. Res. 2016, 49, 2158-2168; Gao et al., J. Am. Chem. Soc., 2010, 132, 10961-10963; May et al., Org. Lett., 2011, 13, 3040-3043.)